Fix Nil pointers in WebSystemdSocket

Signed-off-by: Ethan J. Gallant <ethan.gallant@acquia.com>

Co-authored-by: William Van Hevelingen <William.VanHevelingen@acquia.com>

Co-authored-by: Stephanie Palis <35511514+stephpalis@users.noreply.github.com>

web/tls_config.go

@@ -203,7 +203,11 @@ func ServeMultiple(listeners []net.Listener, server *http.Server, flags *FlagCon
 // WebSystemdSocket in the FlagConfig is true. The FlagConfig is also passed on
 // to ServeMultiple.
 func ListenAndServe(server *http.Server, flags *FlagConfig, logger log.Logger) error {
-	if *flags.WebSystemdSocket {
+	if flags.WebSystemdSocket == nil && (flags.WebListenAddresses == nil || len(*flags.WebListenAddresses) == 0) {
+		return errors.New("no web listen address or systemd socket flag specified")
+	}
+
+	if flags.WebSystemdSocket != nil && *flags.WebSystemdSocket {
 		level.Info(logger).Log("msg", "Listening on systemd activated listeners instead of port listeners.")
 		listeners, err := activation.Listeners()
 		if err != nil {
@@ -214,6 +218,7 @@ func ListenAndServe(server *http.Server, flags *FlagConfig, logger log.Logger) e
 		}
 		return ServeMultiple(listeners, server, flags, logger)
 	}
+
 	listeners := make([]net.Listener, 0, len(*flags.WebListenAddresses))
 	for _, address := range *flags.WebListenAddresses {
 		listener, err := net.Listen("tcp", address)